Since the initial publication of Bednorz and Mueller, "Possible High T.sub.c Superconductivity in the Ba-La-Cu-O System", Z. Phys. B-Condensed Matter 64, p. 189-193 (1986), investigation has revealed a large family of crystalline oxides which exhibit superconductivity at higher temperatures than previously thought possible. The terms "high temperature superconductor" and "high temperature superconductive" are herein employed to describe as a class those crystalline oxides that are capable of exhibiting superconductivity at temperatures greater than 30.degree. K.--i.e., T.sub.o &gt;30.degree. K. Shappirio et al U.S. Pat. No. 4,940,693 and Itozaki et al U.S. Pat. Nos. 4,942,142 and 4,942,152 provide extensive (but not comprehensive) lists of high temperature superconductive crystalline oxides.
While high temperature superconductors can be employed to advantage simply for their high conductivity characteristics, it has been recognized that high temperature superconductive materials can be used to advantage to construct active elements for electrical circuits. One such active element is a Josephson junction device. In such a device conductivity between two superconductive regions is controlled by an interposed region capable of conducting paired electrons between the superconductive regions under one condition of use, but not another. For example, a Josephson junction device may exhibit no measurable impedance at a low current density, but switch to a higher impedance at an increased current density with device impedance being controlled by the interposed region.
A simple form of Josephson junction device is disclosed by Koch et al, "Quantum Interference Devices Made from Superconducting Thin Films", Appl. Phys. Lett. 51(3), Jul. 20, 1987, pp. 200-202. Although Koch et al set out to prepare a Josephson junction device that switched as a result of a region joining two larger superconductive areas, investigation revealed switching to result from Josephson coupling of the superconducting grains.
Other Josephson junction devices have been reported in which two high temperature superconductive crystalline oxide layers are separated by an impedance controlling layer. Low temperature (&lt;30.degree. K.) Josephson junction devices have been reported using niobium as well as organic materials (Bouffard et al U.S. Pat. No. 4,586,062). Josephson junction devices prepared using high temperature superconductive crystalline oxide layers are reported by Rogers et al, "Fabrication of Heteroepitaxial YBa.sub.2 Cu.sub.3 O.sub.7-x -PrBa.sub.2 Cu.sub.3 O.sub.7-x -YBa.sub.2 Cu.sub.3 O.sub.7-x Josephson Devices Grown by Laser Deposition", Appl. Phys. Lett. 55(19), Nov. 6, 1989, pp. 2032-2034; Yamazaki U.S. Pat. No. 4,916,116; Johnson et al U.S. Pat. No. 4,933,317 and Agostinelli et al U.S. Ser. No. 532,479, filed Jun. 4, 1990, A CUBIC PEROVSKITE CRYSTAL STRUCTURE, A PROCESS OF PREPARING THE CRYSTAL STRUCTURE, AND ARTICLES CONSTRUCTED FROM THE CRYSTAL STRUCTURE", commonly assigned.
Various techniques for the deposition of high temperature superconductive crystalline oxide thin films are known. One of the earliest successfully demonstrated techniques of producing a high temperature superconductive crystalline oxide thin film is that of Mir et al U.S. Pat. No. 4,880,770, which thermally decomposed metallorganic precursors. Sputtering has been employed extensively to prepare crystalline oxide thin films, as illustrated by Koinuma et al U.S. Pat. No. 4,902,671; Wu U.S. Pat. No. 4,929,595; Yamaoki et al U.S. Pat. No. 4,935,403; Nishiguchi et al U.S. Pat. No. 4,937,226; Collins et al U.S. Pat. No. 4,960,753 and Gallagher et al U.S. Pat. No. 4,962,086. Vapor deposition techniques have been employed, as illustrated by Fujita et al U.S. Pat. No. 4,925,829 and Kimura et al U.S. Pat. No. 4,931,425. Laser ablation deposition has been demonstrated by Shaw et al U.S. Pat. No. 4,874,741; Rogers et al, cited above; Agostinelli et al, cited above; Dijkkamp et al "Preparation of Y-Ba-Cu Oxide Superconductor Thin Films Using Pulsed Laser Evaporation From High T.sub.c Bulk Material", App. Phys. Lett. 51(8), 24 Aug. 1987, pp. 619-621; and Wu et al "Superlattices of Y-Ba-Cu-O/Y.sub.y -Pr.sub.1-y -Ba-Cu-O Grown by Pulsed Laser Deposition", Appl. Phys. Lett. 56(4), 22 Jan. 1990, pp. 400-402.
Various techniques for patterning high temperature superconductive crystalline oxides have been demonstrated. Mir et al, cited above, suggests laser patterning and patterning using photoresists and etchants. Hayashi et al U.S. Pat. No. 4,891,355 suggests laser addressing a superconductive thin film to convert the film to a nonsuperconductive form. Koch et al, cited above, employed ion implantation to convert a superconductive thin film to an insulative form. Similar ion implantation techniques used for other purposes are disclosed by Yamazaki et al, cited above. Heijman U.S. Pat. No. 4,933,318 discloses ion milling to pattern a superconductive thin film.